The Fort can be visited
Fortress Antwerp-Fort Breendonk

In the Belgian province of Antwerp is Fortress Antwerp-Fort Breendonk, a structure from the early 20th century. Originally designed as part of the Antwerp defense belt, it gained sad notoriety as a detention camp during World War II.
History+
Construction of Fort Breendonk began in 1906, intended to secure the region's defense as part of the Fortress of Antwerp. At the outbreak of World War I, the fort was not yet fully completed, and its original armament included seven armored domes with cannons and howitzers, as well as fourteen rapid-fire cannons for close-range defense. In May 1940, during the Western Campaign, the fortress was captured by the Wehrmacht. Shortly thereafter, in September 1940, the German Secret State Police (Gestapo) established the Breendonk detention camp here. Until its liberation in the autumn of 1944, it served as the center of Gestapo activities in Belgium and Northern France. At least 3,532 people were imprisoned here, of whom only 458 survived the cruel tortures.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: JoJan / CC BY-SA 3.0 via Wikimedia Commons
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 51.0564, 4.3414